Method of manufacturing a semiconductor device and a semiconductor device

ABSTRACT

In a method of manufacturing a semiconductor device, a single crystal oxide layer is formed over a substrate. After the single crystal oxide layer is formed, an isolation structure to define an active region is formed. A gate structure is formed over the single crystal oxide layer in the active region. A source/drain structure is formed.

RELATED APPLICATIONS

This application claims priority of U.S. Provisional Patent ApplicationNo. 62/738,595 filed on Sep. 28, 2018, of which disclosure is entirelyincorporated herein by reference.

BACKGROUND

Conventional complementary metal-oxide-semiconductor (CMOS) technologyis often implemented to fabricate a large number of semiconductordevices, such as metal-oxide-semiconductor field effect transistors(MOSFETs) and bipolar junction transistors (BJTs), at approximately asame level on a single integrated-circuit (IC) chip. In advanced ICchips, transistors are disposed on multiple layers.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIG. 2 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIG. 3 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIG. 4 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIG. 5 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIG. 6 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIG. 7 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIG. 8 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIG. 9 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIG. 10 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIG. 11 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIG. 12 shows one of the various stages of manufacturing a semiconductorFET device according to an embodiment of the present disclosure.

FIGS. 13A and 13B show one of the various stages of manufacturing asemiconductor FET device according to an embodiment of the presentdisclosure.

FIG. 14 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 15 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 16 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 17 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 18 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 19 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 20 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 21 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 22 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 23 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 24 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 25 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 26 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 27 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 28 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 29 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 30 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 31 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 32 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 33 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 34 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 35 shows one of the various stages of manufacturing a semiconductorFET device according to another embodiment of the present disclosure.

FIG. 36A shows one of the various stages of manufacturing asemiconductor FET device according to another embodiment of the presentdisclosure. FIG. 36B shows one of the various stages of manufacturing asemiconductor FET device according to another embodiment of the presentdisclosure.

FIG. 37 shows a cross sectional view of a semiconductor FET deviceaccording to an embodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the invention. Specific embodiments or examples of components andarrangements are described below to simplify the present disclosure.These are, of course, merely examples and are not intended to belimiting. For example, dimensions of elements are not limited to thedisclosed range or values, but may depend upon process conditions and/ordesired properties of the device. Moreover, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed interposing the first and second features, suchthat the first and second features may not be in direct contact. Variousfeatures may be arbitrarily drawn in different scales for simplicity andclarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. In addition, the term“being made of” may mean either “comprising” or “consisting of.” In thepresent disclosure, a phrase “one of A, B and C” means “A, B and/or C”(A, B, C, A and B, A and C, B and C, or A, B and C), and does not meanone element from A, one element from B and one element from C, unlessotherwise described.

For a transistor fabrication process in the back-end of line, there is akey process to form a high quality crystalline semiconductor layer for achannel of the transistor over a non-crystalline layer, such as asilicon oxide layer. The method of manufacturing a crystallinesemiconductor on a silicon oxide layer includes: (a) growing asemiconductor film in an amorphous state followed by high temperatureannealing; and (b) growing a semiconductor layer by using a crystallineseed grown from a crystalline Si substrate. Both of these methods maynot be suitable for a back-end-of-line process because: for method (a),there is a limitation in thermal budget, for example, less than 450° C.,and for method (b), the crystalline seed layer needs to pass throughseveral metal and interlayer dielectric layers.

The present disclosure provides a method to form a high qualitycrystalline semiconductor layer on an amorphous (non-crystal) dielectriclayer. The present disclosure also provides a self-aligned method tofabricate transistors in the areas where polycrystalline or amorphoussemiconductor layers are converted to a crystalline layer having ahigher degree of crystallinity.

In the following embodiments, material, configurations, dimensionsand/or processes of one embodiment may be employed in anotherembodiment, unless otherwise described, and detailed explanation thereofmay be omitted.

FIGS. 1-13A show various stages of manufacturing a semiconductor FETdevice according to an embodiment of the present disclosure. It isunderstood that additional operations can be provided before, during,and after the operations shown by FIGS. 1-13A, and some of theoperations described below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable. Further, in the present disclosure, a source and adrain are interchangeably used and a source/drain refers to at least oneof a source and a drain.

As shown in FIG. 1, a substrate 10 is provided. In some embodiments, thesubstrate 10 includes a single crystal semiconductor layer on at leastits surface portion. The substrate 10 may comprise a single crystalsemiconductor material such as, but not limited to Si, Ge, SiGe, GaAs,InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb and InP. In certainembodiments, the substrate 10 is made of crystalline Si, SiGe or Ge. Thesubstrate 10 may include in its surface region, one or more bufferlayers (not shown) in some embodiments. The buffer layers can serve togradually change the lattice constant from that of the substrate to thatof the source/drain regions. The buffer layers may be formed fromepitaxially grown single crystal semiconductor materials such as, butnot limited to Si, Ge, GeSn, SiGe, GaAs, InSb, GaP, GaSb, InAlAs,InGaAs, GaSbP, GaAsSb, GaN, GaP, and InP. In a particular embodiment,the substrate 10 comprises silicon germanium (SiGe) buffer layersepitaxially grown on the silicon substrate 10. The germaniumconcentration of the SiGe buffer layers may increase from 30 atomic %germanium for the bottom-most buffer layer to 70 atomic % germanium forthe top-most buffer layer.

Further, as shown in FIG. 1, one or more dielectric layers 20 are formedover the substrate 10. In some embodiments, one or more electronicdevices, such as transistors, memories (e.g., dynamic random accessmemory (DRAM), static RAM, magnetic MRAM, and/or phase change RAM), areformed on the substrate 10 and the one or more dielectric layers 20cover the electronic devices. Further, one or more metal wiringstructures are embedded in the dielectric layers 20. The dielectricmaterial for the dielectric layers 20 includes silicon oxide, siliconnitride, silicon oxynitride (SiON), SiCN, fluorine-doped silicate glass(FSG), or a low-K dielectric material, formed by LPCVD (low pressurechemical vapor deposition), plasma-CVD or flowable CVD or any othersuitable film formation method. An annealing operation may be performedafter the formation of the dielectric layer 20. In some embodiments, aplanarization operation, such as a chemical mechanical polishing (CMP)method and/or an etch-back method, is performed to flatten the surfaceof the dielectric layer 20.

Still referring to FIG. 1, a semiconductor layer 30 as a channelsemiconductor material is formed over the dielectric layer 20. Thesemiconductor material for the semiconductor layer 30 includes Si, Ge,SiGe, GaAs, InSb, GaP, GaSb, InAlAs, InGaAs, GaSbP, GaAsSb and InP, insome embodiments. In certain embodiments, the semiconductor layer 30 ismade of Si, SiGe or Ge.

In some embodiments, the semiconductor layer 30 is formed by CVD, ALD orany other suitable film formation method. In some embodiments, the filmformation is performed at a temperature less than about 450° C. In someembodiments, the film formation is performed at a temperature equal toor higher than about 25° C. In some embodiments, a Si₂H₆ gas is used asa source gas of Si and a Ge₂H₆ gas is used as a source gas of Ge. Incertain embodiments, instead of or, in addition to, Ge₂H₆ and/or Si₂H₆,GeH₄ and/or SiH₄ is used. In some embodiments, the semiconductor layer30 is amorphous or polycrystalline. In some embodiments, thesemiconductor layer 30 is appropriately doped with impurities, such asP, As, Sb and/or B. The impurities are doped in-situ during the filmformation, or doped by ion implantation or plasma doping after thesemiconductor layer 30 is formed. A thickness of the semiconductor layer30 is in a range from about 5 nm to about 500 nm in some embodiments,and is in a range from about 10 nm to about 50 nm in other embodiments.

Then, as shown in FIG. 2, a seed layer 40 is formed over thesemiconductor layer 30. In some embodiments, no seed layer is formedunder the semiconductor layer 30. In some embodiments, the seed layer 40is made of metal oxide having a property of being crystalline asdeposited or with a low temperature annealing at about 300° C. to about450° C. In certain embodiments, the seed layer 40 is made of magnesiumoxide (MgO). In some embodiments, the MgO seed layer 40 is singlecrystalline. In other embodiments, the MgO seed layer 40 is polycrystalline or has multiple domains of single crystal. The seed layer 40can be formed by CVD, atomic layer deposition (ALD), physical vapordeposition including sputtering, or any other suitable film formationmethod. A thickness of the seed layer 40 is in a range from about 1 nmto about 100 nm in some embodiments, and is in a range from about 2 nmto about 20 nm in other embodiments. In certain embodiments, thethickness of the seed layer 40 is in a range from about 1 nm to about 10nm. In other embodiments, one of HfO₂, La₂Hf₂O₇, Y₂O₃, SrTiO₃ and HfZrO₂is used as the seed layer 40.

Next, as shown in FIG. 3, the seed layer 40 is patterned into apatterned seed layer 45, by using one or more lithography and etchingoperations. The lithography operation includes ultra violet (UV)lithography, deep UV (DUV) lithography, extreme UV (EUV) lithography,electron beam (e-beam) lithography, and the etching operation includesplasma dry etching. The patterned seed layer 45 corresponds to a gateelectrode of an FET subsequently formed. Thus, the width W1 of thepatterned seed layer 45 corresponds to a gate length of the FET and thepatterned seed layer 45 has a shape corresponding to the gate electrodeof the FET. In some embodiments, the patterned seed layer 45 has a lineshape. The width W1 is in a range from about 5 nm to about 500 nm insome embodiments, and is in a range from about 20 nm to about 200 nm inother embodiments.

Subsequently, as shown in FIGS. 4-7, a crystallization process tocrystalize the semiconductor layer 30 is performed. The crystallizationprocess includes a thermal annealing. In some embodiments, the thermalannealing includes a laser annealing process using nano-second laser,which is transparent to the seed layer. In other embodiments, thethermal annealing includes a low temperature annealing at a temperaturein a range from about 350° C. to 450° C.

As shown in FIGS. 5 and 6, the semiconductor layer 30 starts tocrystalize from the bottom of the patterned seed layer (corresponding toa channel region of the subsequently formed FET) as crystal template. Bycontinuing the thermal annealing process, crystallized portions 35 ofthe semiconductor layer 30 laterally expand into source/drain regions asshown in FIG. 7. In some embodiments, the entire semiconductor layer 30becomes crystal.

Subsequently, as shown in FIG. 8, sidewall spacers 50 are formed onopposite side faces of the patterned seed layer 45. A blanket layer ofan insulating material for sidewall spacers 50 is conformally formed byusing CVD or other suitable methods. The blanket layer is deposited in aconformal manner so that it is formed to have substantially equalthicknesses on vertical surfaces, such as the sidewalls, horizontalsurfaces, and the top of the patterned seed layer 45. In someembodiments, the blanket layer is deposited to a thickness in a rangefrom about 2 nm to about 30 nm. In one embodiment, the insulatingmaterial of the blanket layer is different from the materials of thepatterned seed layer 45, and is made of a silicon nitride-basedmaterial, such as silicon nitride, SiON, SiOCN or SiCN and combinationsthereof. In some embodiments, the blanket layer (sidewall spacers 50) ismade of silicon nitride. The sidewall spacers 50 are formed on oppositeside faces of the patterned seed layer 45, by anisotropic etching, asshown in FIG. 8. The patterned seed layer 45 functions as a dummy gateelectrode in a gate replacement technology.

Then, as shown in FIG. 9, a source region and a drain region are formed.In some embodiments, the source/drain regions 60 include one or moreepitaxial semiconductor layers. The source/drain epitaxial layer 60includes one or more layers of Si, SiP, SiC and SiCP for an n-channelFET or Si, SiGe, Ge for a p-channel FET. For the P-channel FET, boron(B) may also be contained in the source/drain region. The source/drainepitaxial layer 50 is formed by an epitaxial growth method using CVD,ALD or MBE. In some embodiments, the source/drain regions of thecrystallized semiconductor layer 35 are recessed by etching and then thesource/drain epitaxial layer 60 is formed over the recessed source/drainregions of the crystallized semiconductor layer 35. In otherembodiments, one or more ion implantation processes are performed tointroduce impurities into the source/drain regions of the crystallizedsemiconductor layer 35.

Then, a first interlayer dielectric (ILD) layer 65 is formed over thesource/drain epitaxial layer 60 and the patterned seed layer 45. Thematerials for the first ILD layer 65 include compounds comprising Si, O,C and/or H, such as silicon oxide, SiCOH and SiOC. Organic materials,such as polymers, may be used for the first ILD layer 65. After thefirst ILD layer 65 is formed, a planarization operation, such as CMP, isperformed, so that the top portion of the patterned seed layer 45 isexposed, as shown in FIG. 10. In some embodiments, the patterned seedlayer 45 functions as a CMP stop layer. In some embodiments, before thefirst ILD layer 65 is formed, a contact etch stop layer, such as asilicon nitride layer or a silicon oxynitride layer, is formed.

Then, the patterned seed layer 45 is removed, thereby forming a gatespace 47, as shown in FIG. 11. The patterned seed layer 45 can beremoved using plasma dry etching and/or wet etching.

After the patterned seed layer 45 is removed, a gate dielectric layer 70and a gate electrode 75 are formed in the gate space 47, as shown inFIG. 12. In some embodiments, the gate dielectric layer 70 includes oneor more layers of a dielectric material, such as silicon oxide, siliconnitride, or a high-k dielectric material, other suitable dielectricmaterial, and/or combinations thereof. Examples of high-k dielectricmaterials include HfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO, zirconiumoxide, aluminum oxide, titanium oxide, hafnium dioxide-alumina(HfO₂—Al₂O₃) alloy, other suitable high-k dielectric materials, and/orcombinations thereof. In some embodiments, the gate dielectric layer 70includes an interfacial layer formed between the channel layer 35 andthe dielectric material, by using chemical oxidation. The gatedielectric layer 70 may be formed by CVD, ALD or any suitable method. Inone embodiment, the gate dielectric layer 70 is formed using a highlyconformal deposition process such as ALD in order to ensure theformation of a gate dielectric layer having a uniform thickness aroundeach channel layer. The thickness of the gate dielectric layer 70 is ina range from about 1 nm to about 10 nm in one embodiment.

Subsequently, a gate electrode layer 75 is formed on the gate dielectriclayer 70. The gate electrode layer 75 includes one or more layers ofconductive material, such as polysilicon, aluminum, copper, titanium,tantalum, tungsten, cobalt, molybdenum, tantalum nitride, nickelsilicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN, TaC, TaSiN, metalalloys, other suitable materials, and/or combinations thereof. The gateelectrode layer 75 may be formed by CVD, ALD, electro-plating, or othersuitable method. The metals for the gate dielectric layer 75 and thegate electrode layer 75 are also deposited over the upper surface of thefirst ILD layer 65. The material for the gate electrode layer formedover the ILD layer 65 is then planarized by using, for example, CMP,until the top surface of the ILD layer 65 is revealed. In someembodiments, after the planarization operation, the metal gate electrodelayer 77 is recessed and a cap insulating layer (not shown) is formedover the recessed gate electrode layer. The cap insulating layerincludes one or more layers of a silicon nitride-based material, such assilicon nitride. The cap insulating layer can be formed by depositing aninsulating material followed by a planarization operation.

In certain embodiments of the present disclosure, one or more workfunction adjustment layers (not shown) are interposed between the gatedielectric layer 70 and the gate electrode layer 75. The work functionadjustment layers are made of a conductive material such as a singlelayer of TiN, TaN, TaAlC, TiC, TaC, Co, Al, TiAl, HfTi, TiSi, TaSi orTiAlC, or a multilayer of two or more of these materials. For then-channel FET, one or more of TaN, TaAlC, TiN, TiC, Co, TiAl, HfTi, TiSiand TaSi is used as the work function adjustment layer, and for thep-channel FET, one or more of TiAlC, Al, TiAl, TaN, TaAlC, TiN, TiC andCo is used as the work function adjustment layer. The work functionadjustment layer may be formed by ALD, PVD, CVD, e-beam evaporation, orother suitable process. Further, the work function adjustment layer maybe formed separately for the n-channel FET and the p-channel FET whichmay use different metal layers.

Further, as shown in FIG. 13A, a second ILD layer 80 is formed over thefirst ILD layer 65, and conductive contacts 85 passing through thesecond ILD layer 80 or the second and first ILD layers are formed tocontact the gate electrode 75 and the source/drain epitaxial layers 60.Contact openings are formed in the first and/or the second ILD layers.One or more layers of conductive materials are formed in and over thecontact openings and then a planarization operation, such as a CMPoperation, is performed to form conductive contacts 85, as shown in FIG.13A. In some embodiments, the conductive contacts 85 include a linerlayer and a body layer. The liner layer is a barrier layer and/or a glue(adhesion) layer. In some embodiments, a Ti layer is formed on thesource/drain epitaxial layer 55 and a TiN or TaN layer is formed on theTi layer, as the liner layer. The body layer includes one or more layersof Co, Ni, W, Ti, Ta, Cu and Al, or any other suitable material.

It is understood that the FET undergoes further CMOS processes to formvarious features such as contacts/vias, interconnect metal layers,dielectric layers, passivation layers, etc.

In other embodiments, as shown in FIG. 13A, the crystallization processstops when the crystallized portions 35 are formed in the necessaryregions, such as channel regions and the source/drain regions.Accordingly, there is a portion of the non-crystallized semiconductorlayer 30, which is amorphous or poly crystal.

FIGS. 14-23 show various stages of manufacturing a semiconductor FETdevice according to an embodiment of the present disclosure. It isunderstood that additional operations can be provided before, during,and after the operations shown by FIGS. 14-23, and some of theoperations described below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable.

Similar to FIGS. 1 and 2, a seed layer 40 is formed over a semiconductorlayer 30. Next, as shown in FIG. 14, the seed layer 40 is patterned intomultiple patterned seed layers 45, by using one or more lithography andetching operations. The lithography operation includes UV lithography,DUV lithography, EUV lithography, e-beam lithography, and the etchingoperation includes plasma dry etching. The patterned seed layers 45correspond to gate electrodes of FETs subsequently formed. In someembodiments, the patterned seed layers 45 have a line shape. The widthof the patterned seed layers 45 are in a range from about 5 nm to about500 nm in some embodiments, and is in a range from about 20 nm to about200 nm in other embodiments.

Subsequently, as shown in FIGS. 15-18, a crystallization process tocrystalize the semiconductor layer 30 is performed. The crystallizationprocess includes a thermal annealing. In some embodiments, the thermalannealing includes a laser annealing process using nano-second laser,which is transparent to the seed layer. In other embodiments, thethermal annealing includes a low temperature annealing at a temperaturein a range from about 350° C. to 450° C.

As shown in FIGS. 16 and 17, the semiconductor layer 30 starts tocrystalize from the bottoms of the patterned seed layers 45(corresponding to channel regions of the subsequently formed FETs) ascrystal template. By continuing the thermal annealing process,crystallized portions 35 of the semiconductor layer 30 laterally expandinto source/drain regions as shown in FIG. 17.

As shown in FIG. 18, each of front portions of the crystallizedsemiconductor layers 35 meet the adjacent front portion of thecrystallized semiconductor layers 35, creating a grain boundary 37.

Subsequently, as shown in FIG. 19, sidewall spacers 50 are formed onopposite side faces of the patterned seed layers 45. A blanket layer ofan insulating material for sidewall spacers 50 is conformally formed byusing CVD or other suitable methods. The blanket layer is deposited in aconformal manner so that it is formed to have substantially equalthicknesses on vertical surfaces, such as the sidewalls, horizontalsurfaces, and the top of the patterned seed layers 45. In someembodiments, the blanket layer is deposited to a thickness in a rangefrom about 2 nm to about 30 nm. In one embodiment, the insulatingmaterial of the blanket layer is different from the materials of thepatterned seed layers 45, and is made of a silicon nitride-basedmaterial, such as silicon nitride, SiON, SiOCN or SiCN and combinationsthereof. In some embodiments, the blanket layer (sidewall spacers 50) ismade of silicon nitride. The sidewall spacers 50 are formed on oppositeside faces of the patterned seed layers 45, by anisotropic etching, asshown in FIG. 8. The patterned seed layers 45 function as a dummy gateelectrode in a gate replacement technology.

Then, as shown in FIG. 20, source regions and drain regions are formed.In some embodiments, the source/drain regions 60 include one or moreepitaxial semiconductor layers. The source/drain epitaxial layers 60include one or more layers of Si, SiP, SiC and SiCP for an n-channel FETor Si, SiGe, Ge for a p-channel FET. For the P-channel FET, boron (B)may also be contained in the source/drain region. The source/drainepitaxial layer 50 is formed by an epitaxial growth method using CVD,ALD or MBE. In some embodiments, the source/drain regions of thecrystallized semiconductor layer 35 are recessed by etching and then thesource/drain epitaxial layers 60 are formed over the recessedsource/drain regions of the crystallized semiconductor layer 35. Inother embodiments, one or more ion implantation processes are performedto introduce impurities into the source/drain regions of thecrystallized semiconductor layer 35. In some embodiments, thesource/drain epitaxial layers 60 fully fill spaces between adjacentdummy gate electrodes (patterned seed layers 45), and in otherembodiments, the source/drain epitaxial layers 60 only partially fillspaces between adjacent dummy gate electrodes.

Then, a first interlayer dielectric (ILD) layer 65 is formed over thesource/drain epitaxial layers 60 and the patterned seed layers 45. Thematerials for the first ILD layer 65 include compounds comprising Si, O,C and/or H, such as silicon oxide, SiCOH and SiOC. Organic materials,such as polymers, may be used for the first ILD layer 65. After thefirst ILD layer 65 is formed, a planarization operation, such as CMP, isperformed, so that the top portions of the patterned seed layers 45 areexposed, as shown in FIG. 21. In some embodiments, the patterned seedlayers 45 function as a CMP stop layer. In some embodiments, before thefirst ILD layer 65 is formed, a contact etch stop layer, such as asilicon nitride layer or a silicon oxynitride layer, is formed.

Then, the patterned seed layers 45 are removed, thereby forming gatespaces 47, as shown in FIG. 22. The patterned seed layers 45 can beremoved using plasma dry etching and/or wet etching.

After the patterned seed layers 45 are removed, a gate dielectric layer70 and a gate electrode 75 are formed in each of the gate spaces 47, asshown in FIG. 23. In some embodiments, the gate dielectric layer 70includes one or more layers of a dielectric material, such as siliconoxide, silicon nitride, or a high-k dielectric material, other suitabledielectric material, and/or combinations thereof. Examples of high-kdielectric materials include HfO₂, HfSiO, HfSiON, HfTaO, HfTiO, HfZrO,zirconium oxide, aluminum oxide, titanium oxide, hafnium dioxide-alumina(HfO₂—Al₂O₃) alloy, other suitable high-k dielectric materials, and/orcombinations thereof. In some embodiments, the gate dielectric layer 70includes an interfacial layer formed between the channel layer 35 andthe dielectric material, by using chemical oxidation. The gatedielectric layer 70 may be formed by CVD, ALD or any suitable method. Inone embodiment, the gate dielectric layer 70 is formed using a highlyconformal deposition process such as ALD in order to ensure theformation of a gate dielectric layer having a uniform thickness aroundeach channel layer. The thickness of the gate dielectric layer 70 is ina range from about 1 nm to about 10 nm in one embodiment.

Subsequently, a gate electrode layer 75 is formed on the gate dielectriclayer 70. The gate electrode layer 75 includes one or more layers ofconductive material, such as polysilicon, aluminum, copper, titanium,tantalum, tungsten, cobalt, molybdenum, tantalum nitride, nickelsilicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN, TaC, TaSiN, metalalloys, other suitable materials, and/or combinations thereof. The gateelectrode layer 75 may be formed by CVD, ALD, electro-plating, or othersuitable method. The metals for the gate dielectric layer 70 and thegate electrode layer 75 are also deposited over the upper surface of thefirst ILD layer 65. The material for the gate electrode layer formedover the ILD layer 65 is then planarized by using, for example, CMP,until the top surface of the ILD layer 65 is revealed. In someembodiments, after the planarization operation, the metal gate electrodelayer 77 is recessed and a cap insulating layer (not shown) is formedover the recessed gate electrode layer. The cap insulating layerincludes one or more layers of a silicon nitride-based material, such assilicon nitride. The cap insulating layer can be formed by depositing aninsulating material followed by a planarization operation.

In certain embodiments of the present disclosure, one or more workfunction adjustment layers (not shown) are interposed between the gatedielectric layer 70 and the gate electrode layer 75. The work functionadjustment layers are made of a conductive material such as a singlelayer of TiN, TaN, TaAlC, TiC, TaC, Co, Al, TiAl, HfTi, TiSi, TaSi orTiAlC, or a multilayer of two or more of these materials. For then-channel FET, one or more of TaN, TaAlC, TiN, TiC, Co, TiAl, HfTi, TiSiand TaSi is used as the work function adjustment layer, and for thep-channel FET, one or more of TiAlC, Al, TiAl, TaN, TaAlC, TiN, TiC andCo is used as the work function adjustment layer. The work functionadjustment layer may be formed by ALD, PVD, CVD, e-beam evaporation, orother suitable process. Further, the work function adjustment layer maybe formed separately for the n-channel FET and the p-channel FET whichmay use different metal layers.

Further, similar to FIG. 13A, a second ILD layer is formed over thefirst ILD layer, and conductive contacts passing through the second ILDlayer or the second and first ILD layers are formed to contact the gateelectrode and the source/drain epitaxial layers.

In other embodiments, the crystallization process stops before each offront portions of the crystallized semiconductor layers 35 meet theadjacent front portion of the crystallized semiconductor layers 35. Insuch a case, a portion of non-crystallized semiconductor layer 30remains between adjacent FETs.

It is understood that the FET undergoes further CMOS processes to formvarious features such as contacts/vias, interconnect metal layers,dielectric layers, passivation layers, etc.

FIGS. 24-36A show various stages of manufacturing a semiconductor FETdevice according to an embodiment of the present disclosure. It isunderstood that additional operations can be provided before, during,and after the operations shown by FIGS. 24-36A, and some of theoperations described below can be replaced or eliminated, for additionalembodiments of the method. The order of the operations/processes may beinterchangeable.

Similar to FIG. 1, a semiconductor layer 30 is formed over a dielectriclayer 20 disposed over a substrate 10, as shown in FIG. 25. Then,similar to FIG. 2, a seed layer 40 is formed over the semiconductorlayer 30, as shown in FIG. 25. In some embodiments, the seed layer 40 ismade of metal oxide having a property of being crystalline as depositedor with a low temperature annealing at about 350° C. to about 450° C. Incertain embodiments, the seed layer 40 is made of magnesium oxide (MgO).In some embodiments, the MgO seed layer 40 is single crystalline. Inother embodiments, the MgO seed layer 40 is poly crystalline or hasmultiple domains of single crystal. The seed layer 40 can be formed byCVD, atomic layer deposition (ALD), physical vapor deposition includingsputtering, or any other suitable film formation method. A thickness ofthe seed layer 40 is in a range from about 1 nm to about 100 nm in someembodiments, and is in a range from about 2 nm to about 20 nm in otherembodiments. In certain embodiments, the thickness of the seed layer 40is in a range from about 1 nm to about 10 nm.

Then, as shown in FIG. 26, a dummy gate layer 90 is formed over the seedlayer 45. In some embodiments, the dummy gate layer 90 is made of polysilicon or amorphous silicon. Other semiconductor material or dielectricmaterial, which can be selectively removed with respect to an ILD layerand sidewall spacers, may also be used. A thickness of the dummy gatelayer 90 is in a range from about 50 nm to about 500 nm in someembodiments, and is in a range from about 100 nm to 200 nm in otherembodiments. The dummy gate layer 90 can be formed by CVD, atomic layerdeposition (ALD), physical vapor deposition including sputtering, or anyother suitable film formation method.

Next, as shown in FIG. 27, the dummy gate layer 90 and the seed layer 40are patterned into multiple patterned dummy gate layer 95 and patternedseed layers 45, by using one or more lithography and etching operations.The lithography operation includes UV lithography, DUV lithography, EUVlithography, e-beam lithography, and the etching operation includesplasma dry etching. The patterned dummy gate layer 95 and patterned seedlayers 45 correspond to gate electrodes of FETs subsequently formed. Insome embodiments, the patterned dummy gate layer 95 and patterned seedlayers 45 have a line shape. The width of the patterned dummy gate layer95 and patterned seed layers 45 are in a range from about 5 nm to about500 nm in some embodiments, and is in a range from about 20 nm to about200 nm in other embodiments.

Subsequently, as shown in FIGS. 28-31, a crystallization process tocrystalize the semiconductor layer 30 is performed. The crystallizationprocess includes a thermal annealing. In some embodiments, the thermalannealing includes a laser annealing process using nano-second laser,which is transparent to the seed layer. In other embodiments, thethermal annealing includes a low temperature annealing at a temperaturein a range from about 350° C. to 450° C.

As shown in FIGS. 29 and 30, the semiconductor layer 30 starts tocrystalize from the bottoms of the patterned seed layers 45(corresponding to channel regions of the subsequently formed FETs) ascrystal template. By continuing the thermal annealing process,crystallized portions 35 of the semiconductor layer 30 laterally expandinto source/drain regions as shown in FIG. 30.

As shown in FIG. 31, each of front portions of the crystallizedsemiconductor layers 35 meet the adjacent front portion of thecrystallized semiconductor layers 35, creating a grain boundary 37.

Subsequently, as shown in FIG. 32, sidewall spacers 50 are formed onopposite side faces of the patterned dummy gate layer 95 and patternedseed layers 45. A blanket layer of an insulating material for sidewallspacers 50 is conformally formed by using CVD or other suitable methods.The blanket layer is deposited in a conformal manner so that it isformed to have substantially equal thicknesses on vertical surfaces,such as the sidewalls, horizontal surfaces, and the top of the patterneddummy gate layer 95 and patterned seed layers 45. In some embodiments,the blanket layer is deposited to a thickness in a range from about 2 nmto about 30 nm. In one embodiment, the insulating material of theblanket layer is different from the materials of the patterned dummygate layer 95 and patterned seed layers 45, and is made of a siliconnitride-based material, such as silicon nitride, SiON, SiOCN or SiCN andcombinations thereof. In some embodiments, the blanket layer (sidewallspacers 50) is made of silicon nitride. The sidewall spacers 50 areformed on opposite side faces of the patterned dummy gate layer 95 andpatterned seed layers 45, by anisotropic etching, as shown in FIG. 8.The patterned dummy gate layer 95 and patterned seed layers 45 functionas a dummy gate electrode in a gate replacement technology.

Then, as shown in FIG. 33, source regions and drain regions are formed.In some embodiments, the source/drain regions 60 include one or moreepitaxial semiconductor layers. The source/drain epitaxial layers 60include one or more layers of Si, SiP, SiC and SiCP for an n-channel FETor Si, SiGe, Ge for a p-channel FET. For the P-channel FET, boron (B)may also be contained in the source/drain region. The source/drainepitaxial layer 50 is formed by an epitaxial growth method using CVD,ALD or MBE. In some embodiments, the source/drain regions of thecrystallized semiconductor layer 35 are recessed by etching and then thesource/drain epitaxial layers 60 are formed over the recessedsource/drain regions of the crystallized semiconductor layer 35. Inother embodiments, one or more ion implantation processes are performedto introduce impurities into the source/drain regions of thecrystallized semiconductor layer 35. In some embodiments, thesource/drain epitaxial layers 60 fully fill spaces between adjacentdummy gate electrodes (patterned dummy gate layer 95 and patterned seedlayers 45), and in other embodiments, the source/drain epitaxial layers60 only partially fill spaces between adjacent dummy gate electrodes.

Then, a first interlayer dielectric (ILD) layer 65 is formed over thesource/drain epitaxial layers 60 and the patterned dummy gate layer 95and patterned seed layers 45. The materials for the first ILD layer 65include compounds comprising Si, O, C and/or H, such as silicon oxide,SiCOH and SiOC. Organic materials, such as polymers, may be used for thefirst ILD layer 65. After the first ILD layer 65 is formed, aplanarization operation, such as CMP, is performed, so that the topportions of the patterned dummy gate layer 95 and patterned seed layers45 are exposed, as shown in FIG. 34. In some embodiments, the patterneddummy gate layer 95 functions as a CMP stop layer. In some embodiments,before the first ILD layer 65 is formed, a contact etch stop layer, suchas a silicon nitride layer or a silicon oxynitride layer, is formed.

Then, the patterned dummy gate layer 95 and patterned seed layers 45 areremoved, thereby forming gate spaces 47, as shown in FIG. 22. Thepatterned dummy gate layer 95 and patterned seed layers 45 can beremoved using plasma dry etching and/or wet etching. When the patterneddummy gate layer 95 is polysilicon or amorphous silicon, a wet etchantsuch as a tetramethylammonium hydroxide (TMAH) solution can be used toselectively remove the dummy gate layer. The patterned seed layers 45are thereafter removed using plasma dry etching and/or wet etching.

After the patterned dummy gate layer 95 and patterned seed layers 45 areremoved, a gate dielectric layer 70 and a gate electrode 75 are formedin each of the gate spaces 47, as shown in FIG. 36A. In someembodiments, the gate dielectric layer 70 includes one or more layers ofa dielectric material, such as silicon oxide, silicon nitride, or ahigh-k dielectric material, other suitable dielectric material, and/orcombinations thereof. Examples of high-k dielectric materials includeHfO₂, HfSiO, HfSiON, HMO, HfTiO, HfZrO, zirconium oxide, aluminum oxide,titanium oxide, hafnium dioxide-alumina (HfO₂—Al₂O₃) alloy, othersuitable high-k dielectric materials, and/or combinations thereof. Insome embodiments, the gate dielectric layer 70 includes an interfaciallayer formed between the channel layer 35 and the dielectric material,by using chemical oxidation. The gate dielectric layer 70 may be formedby CVD, ALD or any suitable method. In one embodiment, the gatedielectric layer 70 is formed using a highly conformal depositionprocess such as ALD in order to ensure the formation of a gatedielectric layer having a uniform thickness around each channel layer.The thickness of the gate dielectric layer 70 is in a range from about 1nm to about 10 nm in one embodiment.

Subsequently, a gate electrode layer 75 is formed on the gate dielectriclayer 70. The gate electrode layer 70 includes one or more layers ofconductive material, such as polysilicon, aluminum, copper, titanium,tantalum, tungsten, cobalt, molybdenum, tantalum nitride, nickelsilicide, cobalt silicide, TiN, WN, TiAl, TiAlN, TaCN, TaC, TaSiN, metalalloys, other suitable materials, and/or combinations thereof. The gateelectrode layer 75 may be formed by CVD, ALD, electro-plating, or othersuitable method. The metals for the gate dielectric layer 70 and thegate electrode layer 75 are also deposited over the upper surface of thefirst ILD layer 65. The material for the gate electrode layer formedover the ILD layer 65 is then planarized by using, for example, CMP,until the top surface of the ILD layer 65 is revealed. In someembodiments, after the planarization operation, the metal gate electrodelayer 77 is recessed and a cap insulating layer (not shown) is formedover the recessed gate electrode layer. The cap insulating layerincludes one or more layers of a silicon nitride-based material, such assilicon nitride. The cap insulating layer can be formed by depositing aninsulating material followed by a planarization operation.

In certain embodiments of the present disclosure, one or more workfunction adjustment layers (not shown) are interposed between the gatedielectric layer 70 and the gate electrode layer 75. The work functionadjustment layers are made of a conductive material such as a singlelayer of TiN, TaN, TaAlC, TiC, TaC, Co, Al, TiAl, HfTi, TiSi, TaSi orTiAlC, or a multilayer of two or more of these materials. For then-channel FET, one or more of TaN, TaAlC, TiN, TiC, Co, TiAl, HfTi, TiSiand TaSi is used as the work function adjustment layer, and for thep-channel FET, one or more of TiAlC, Al, TiAl, TaN, TaAlC, TiN, TiC andCo is used as the work function adjustment layer. The work functionadjustment layer may be formed by ALD, PVD, CVD, e-beam evaporation, orother suitable process. Further, the work function adjustment layer maybe formed separately for the n-channel FET and the p-channel FET whichmay use different metal layers.

Further, similar to FIG. 13A, a second ILD layer is formed over thefirst ILD layer, and conductive contacts passing through the second ILDlayer or the second and first ILD layers are formed to contact the gateelectrode and the source/drain epitaxial layers. As shown in FIG. 13A,the manufactured FET is a thin film transistor (TFT) in someembodiments.

In other embodiments, the crystallization process stops before each offront portions of the crystallized semiconductor layers 35 meet theadjacent front portion of the crystallized semiconductor layers 35. Insuch a case, a portion of non-crystallized semiconductor layer 30remains between adjacent FETs, as shown in FIG. 36B.

It is understood that the FET undergoes further CMOS processes to formvarious features such as contacts/vias, interconnect metal layers,dielectric layers, passivation layers, etc.

FIG. 37 shows a cross sectional view of a semiconductor device accordingto an embodiment of the present disclosure. As shown in FIG. 37, a lowerlayer device 100 is formed over a substrate. The lower layer devices 100includes one or more fin field effect transistors (FinFETs),gate-all-around FET (GAA FET), planar FETs, vertical FETs or any otherelectronic devices. FIG. 37 also shows an upper layer device 200disposed over the lower layer device 100. In some embodiments, one ormore ILD layers, metal wiring layers and/or via contacts are disposedbetween the lower layer device 100 and the upper layer device 200. Insome embodiments, the upper layer device 200 includes one or more FETsmanufactured by the aforementioned embodiments of the presentdisclosure.

The various embodiments or examples described herein offer severaladvantages over the existing art. For example, in the presentdisclosure, a crystallization process of a non-crystal semiconductorlayer is performed using a patterned seed layer formed on thenon-crystal semiconductor layer (a top seed layer). Since thecrystallization of the non-crystal semiconductor layer starts from thebottom of the patterned seed layer and the patterned seed layer isutilized as a dummy gate, it is possible to utilize the initiallycrystalized portion (closer to the seed layer) having a highercrystalline quality, as a channel region of an FET. In other words, thebest crystalline portions can be utilized as channel regions in aself-aligned manner. Further, by utilizing the seed layer as a dummygate for a gate replacement process, it is possible to suppress anincrease in operation steps of manufacturing the semiconductor device.The operations of the present disclosure is compatible withback-end-of-line processes of the semiconductor manufacturing.

It will be understood that not all advantages have been necessarilydiscussed herein, no particular advantage is required for allembodiments or examples, and other embodiments or examples may offerdifferent advantages.

In accordance with an aspect of the present disclosure, in a method ofmanufacturing a semiconductor device, a semiconductor layer is formed ona dielectric layer disposed over a substrate. A seed layer is formed onthe semiconductor layer. The seed layer is patterned into a patternedseed layer. Aa crystallization operation is performed on thesemiconductor layer using the patterned seed layer as a seed ofcrystallization, thereby forming a crystallized semiconductor layer. Inone or more of the foregoing and the following embodiments, the seedlayer is MgO. In one or more of the foregoing and the followingembodiments, the semiconductor layer is amorphous or poly crystal. Inone or more of the foregoing and the following embodiments, thesemiconductor layer is one of Si, SiGe and Ge. In one or more of theforegoing and the following embodiments, a thickness of the seed layeris in a range from 1 nm to 10 nm. In one or more of the foregoing andthe following embodiments, a thickness of the semiconductor layer is ina range from 10 nm to 50 nm. In one or more of the foregoing and thefollowing embodiments, the crystallization operation includes a thermalannealing at a temperature from 350° C. to 450° C. or a laser annealing.In one or more of the foregoing and the following embodiments, sidewallspacers are formed on opposing side faces of the patterned seed layer. Asource/drain structure is formed. An interlayer dielectric (ILD) layeris formed over the sidewall spacers, the patterned seed layer and thesource/drain structure. After the ILD layer is formed, the patternedseed layer is removed, thereby forming a gate space. A gate dielectriclayer and a gate electrode layer are formed in the gate space.

In accordance with another aspect of the present disclosure, in methodof manufacturing a semiconductor device, a semiconductor layer is formedon a dielectric layer disposed over a substrate. A seed layer is formedon the semiconductor layer. The seed layer is patterned into patternedseed layers. A crystallization operation is performed on thesemiconductor layer using the patterned seed layers as a seed ofcrystallization, thereby forming crystallized semiconductor layers. Inone or more of the foregoing and the following embodiments, the seedlayer is MgO. In one or more of the foregoing and the followingembodiments, the semiconductor layer is amorphous or poly crystal of oneof Si, SiGe and Ge. In one or more of the foregoing and the followingembodiments, the crystallization operation includes a thermal annealingat a temperature from 350° C. to 450° C. or a laser annealing. In one ormore of the foregoing and the following embodiments, sidewall spacersare formed on opposing side faces of the patterned seed layers. Asource/drain structure is formed. An interlayer dielectric (ILD) layeris formed over the sidewall spacers, the patterned seed layers and thesource/drain structure. After the ILD layer is formed, the patternedseed layers are removed, thereby forming gate spaces. A gate dielectriclayer and a gate electrode layer are formed in each of the gate spaces.In one or more of the foregoing and the following embodiments, thecrystallization operation is performed such that a front portion of acrystallized semiconductor layer under one of the seed layers meets afront portion of a crystallized semiconductor layer under another of theseed layers adjacent to the one of the seed layers, thereby forming agrain boundary. In one or more of the foregoing and the followingembodiments, the crystallization operation is stopped before a frontportion of a crystallized semiconductor layer under one of the seedlayers meets a front portion of a crystallized semiconductor layer underanother of the seed layers adjacent to the one of the seed layers.

In accordance with another aspect of the present disclosure, in a methodof manufacturing a semiconductor device, a semiconductor layer is formedon a dielectric layer disposed over a substrate. A seed layer is formedon the semiconductor layer. A dummy gate layer is formed on the seedlayer. The dummy gate layer and the seed layer are formed into apatterned dummy gate layer and a patterned seed layer. A crystallizationoperation is performed on the semiconductor layer using the patternedseed layer as a seed of crystallization, thereby forming a crystallizedsemiconductor layer. In one or more of the foregoing and the followingembodiments, the dummy gate layer is amorphous or poly crystal of one ofSi, SiGe and Ge. In one or more of the foregoing and the followingembodiments, a thickness of the dummy gate layer is in a range from 50nm to 200 nm. In one or more of the foregoing and the followingembodiments, the seed layer is MgO. In one or more of the foregoing andthe following embodiments, sidewall spacers are formed on opposing sidefaces of the patterned dummy gate layer and the patterned seed layer. Asource/drain structure is formed. An interlayer dielectric (ILD) layeris formed over the sidewall spacers, the patterned dummy gate layer andthe source/drain structure. After the ILD layer is formed, the patterneddummy gate layer and the patterned seed layer are removed, therebyforming a gate space. A gate dielectric layer and a gate electrode layerare formed in the gate space.

In accordance with one aspect of the present disclosure, a semiconductordevice includes a channel formed as a part of a semiconductor layerdisposed on a dielectric layer, a gate dielectric layer disposed overthe channel, a gate electrode layer disposed over the gate dielectriclayer, sidewall spacers disposed on opposite side faces of the gateelectrode layer, and a source and a drain. The semiconductor layerincludes a crystal portion as the channel and a non-crystal portion. Inone or more of the foregoing and the following embodiments, thesemiconductor device further includes one or more transistors covered bythe dielectric layer. In one or more of the foregoing and the followingembodiments, the one or more transistors include fin field effecttransistors. In one or more of the foregoing and the followingembodiments, the semiconductor layer is made of one of Si, SiGe and Ge.In one or more of the foregoing and the following embodiments, athickness of the semiconductor layer is in a range from 10 nm to 50 nm.

In accordance with another aspect of the present disclosure, asemiconductor device includes an electronic device disposed on asubstrate, one or more dielectric layers disposed over the electronicdevice, thin film transistors disposed on an uppermost layer of the oneor more dielectric layers. Each of the thin film transistor includes achannel formed as a part of a semiconductor layer disposed on theuppermost layer, a gate dielectric layer disposed over the channel, agate electrode layer disposed over the gate dielectric layer, sidewallspacers disposed on opposite side faces of the gate electrode layer, anda source and a drain. The semiconductor layer is single crystal, and agrain boundary exists between the semiconductor layer of one of the thinfilm transistors and the semiconductor layer of another of the thin filmtransistors adjacent to the one of the thin film transistors. In one ormore of the foregoing and the following embodiments, the electronicdevice is a transistor. In one or more of the foregoing and thefollowing embodiments, the transistor is one of a fin field effecttransistor and a gate-all-around transistor. In one or more of theforegoing and the following embodiments, the semiconductor layer is madeof one of Si, SiGe and Ge. In one or more of the foregoing and thefollowing embodiments, the uppermost layer is made of silicon oxide. Inone or more of the foregoing and the following embodiments, a thicknessof the semiconductor layer is in a range from 10 nm to 50 nm. In one ormore of the foregoing and the following embodiments, the source and thedrain includes an epitaxial semiconductor layer. In one or more of theforegoing and the following embodiments, the epitaxial semiconductorlayer is in contact with one of the sidewall spacers of the one of thethin film transistors and one of the sidewall spacers of the another oneof the thin film transistors.

In accordance with another aspect of the present disclosure, asemiconductor device includes an electronic device disposed on asubstrate, one or more dielectric layers disposed over the electronicdevice, and thin film transistors disposed on an uppermost layer of theone or more dielectric layers. Each of the thin film transistorincludes, a channel formed as a part of a semiconductor layer disposedon the uppermost layer, a gate dielectric layer disposed over thechannel, a gate electrode layer disposed over the gate dielectric layer,sidewall spacers disposed on opposite side faces of the gate electrodelayer, and a source and a drain. The channel is single crystal, and anon-crystalline semiconductor layer made of a same material as thesemiconductor layer exists between the semiconductor layer of one of thethin film transistors and the semiconductor layer of another of the thinfilm transistors adjacent to the one of the thin film transistors. Inone or more of the foregoing and the following embodiments, theelectronic device is a transistor. In one or more of the foregoing andthe following embodiments, the transistor is one of a fin field effecttransistor and a gate-all-around transistor. In one or more of theforegoing and the following embodiments, the semiconductor layer is madeof one of Si, SiGe and Ge. In one or more of the foregoing and thefollowing embodiments, a thickness of the semiconductor layer is in arange from 10 nm to 50 nm. In one or more of the foregoing and thefollowing embodiments, the source and the drain includes an epitaxialsemiconductor layer. In one or more of the foregoing and the followingembodiments, the epitaxial semiconductor layer is in contact with one ofthe sidewall spacers of the one of the thin film transistors and one ofthe sidewall spacers of the another one of the thin film transistors.

The foregoing outlines features of several embodiments or examples sothat those skilled in the art may better understand the aspects of thepresent disclosure. Those skilled in the art should appreciate that theymay readily use the present disclosure as a basis for designing ormodifying other processes and structures for carrying out the samepurposes and/or achieving the same advantages of the embodiments orexamples introduced herein. Those skilled in the art should also realizethat such equivalent constructions do not depart from the spirit andscope of the present disclosure, and that they may make various changes,substitutions, and alterations herein without departing from the spiritand scope of the present disclosure.

What is claimed is:
 1. A method of manufacturing a semiconductor device,the method comprising: forming a semiconductor layer on a dielectriclayer disposed over a substrate; forming a seed layer on thesemiconductor layer; patterning the seed layer into a patterned seedlayer; and performing a crystallization operation on the semiconductorlayer using the patterned seed layer as a seed of crystallization,thereby forming a crystallized semiconductor layer.
 2. The method ofclaim 1, wherein the seed layer is MgO.
 3. The method of claim 1,wherein the semiconductor layer is amorphous or poly crystal.
 4. Themethod of claim 3, wherein the semiconductor layer is one of Si, SiGeand Ge.
 5. The method of claim 1, wherein a thickness of the seed layeris in a range from 1 nm to 10 nm.
 6. The method of claim 1, wherein athickness of the semiconductor layer is in a range from 10 nm to 50 nm.7. The method of claim 1, wherein the crystallization operation includesa thermal annealing at a temperature from 350° C. to 450° C. or a laserannealing.
 8. The method of claim 1, further comprising: formingsidewall spacers on opposing side faces of the patterned seed layer;forming a source/drain structure; forming an interlayer dielectric (ILD)layer over the sidewall spacers, the patterned seed layer and thesource/drain structure; after the ILD layer is formed, removing thepatterned seed layer, thereby forming a gate space; and forming a gatedielectric layer and a gate electrode layer in the gate space.
 9. Amethod of manufacturing a semiconductor device, the method comprising:forming an amorphous or a poly crystal semiconductor layer on adielectric layer disposed over a substrate; forming a seed layer on thesemiconductor layer; patterning the seed layer into multiple patternedseed layers; and performing a crystallization operation on thesemiconductor layer using the patterned seed layers as a seed ofcrystallization, thereby forming multiple single crystallinesemiconductor layers over the dielectric layer.
 10. The method of claim9, wherein the seed layer is MgO.
 11. The method of claim 9, wherein thesemiconductor layer is amorphous or poly crystal of one of Si, SiGe andGe.
 12. The method of claim 9, wherein the crystallization operationincludes a thermal annealing at a temperature from 350° C. to 450° C. ora laser annealing.
 13. The method of claim 9, further comprising:forming sidewall spacers on opposing side faces of the patterned seedlayers; forming a source/drain structure; forming an interlayerdielectric (ILD) layer over the sidewall spacers, the patterned seedlayers and the source/drain structure; after the ILD layer is formed,removing the patterned seed layers, thereby forming gate spaces; andforming a gate dielectric layer and a gate electrode layer in each ofthe gate spaces.
 14. The method of claim 9, wherein the crystallizationoperation is performed such that a front portion of a crystallizedsemiconductor layer under one of the seed layers meets a front portionof a crystallized semiconductor layer under another of the seed layersadjacent to the one of the seed layers, thereby forming a grainboundary.
 15. The method of claim 9, wherein the crystallizationoperation is stopped before a front portion of a crystallizedsemiconductor layer under one of the seed layers meets a front portionof a crystallized semiconductor layer under another of the seed layersadjacent to the one of the seed layers.
 16. A semiconductor devicecomprising: an electronic device disposed on a substrate; one or moredielectric layers disposed over the electronic device; and thin filmtransistors disposed on an uppermost layer of the one or more dielectriclayers, wherein: each of the thin film transistor includes: a channelformed as a part of a semiconductor layer disposed on the uppermostlayer; a gate dielectric layer disposed over the channel; a gateelectrode layer disposed over the gate dielectric layer; sidewallspacers disposed on opposite side faces of the gate electrode layer; anda source and a drain, the channel is single crystal, and a grainboundary exists between the semiconductor layer of one of the thin filmtransistors and the semiconductor layer of another of the thin filmtransistors adjacent to the one of the thin film transistors.
 17. Thesemiconductor device of claim 16, wherein the electronic device is atransistor.
 18. The semiconductor device of claim 17, wherein thetransistor is one of a fin field effect transistor and a gate-all-aroundtransistor.
 19. The semiconductor device of claim 16, wherein thesemiconductor layer is made of one of Si, SiGe and Ge.
 20. Thesemiconductor device of claim 16, wherein the uppermost layer is made ofsilicon oxide.